Method of producing assembled camshafts

ABSTRACT

A method of producing assembled camshafts from a tubular member and components slid on to same and having through-holes and outer functional faces, wherein the components are provided with through-holes which have been machined by non-chip-forming operations and on which an outer contour is preferably finish-machined; wherein the tubular member can be clamped in so as to be centred on a reference axis B; wherein the components are slid on and are centred via their outer contour on the reference axis of the clamping means of the tubular member; wherein, between the through-holes and the tubular member, a compensating and joining gap is provided and wherein; between the components and the tubular member with material being added, a material locking connection or a press fit connection is provided by expanding the tubular member.

BACKGROUND OF THE INVENTION

The invention relates to a method of producing assembled camshafts from one or more tubular members and components. Each component can be slid on to a tubular member, and each is provided with a through-hole and an outer functional face, more particularly cam discs and bearing races. Furthermore, one or more of the components can comprise pulse generator cams, camshaft adjusting elements, driving pinions, and like devices. Assembled camshafts according to the invention can be advantageous in that the tubular member and components, such as the slid-on camshafts or bearing races, can be optimised in respect of their functional requirements. For example, it is possible to use a fracture-resistant tubular member with an adequate torsional elasticity with cams or bearing races comprised of material which can be forged, cast or includes sintered material, to achieve highly resistant functional faces of the assembled camshaft. In addition, an assembled camshaft comprises considerable weight advantages as compared to solid shafts, such as they may be required for modern lightweight engines.

For producing one or more connections between a tubular shaft and components such as cam discs, bearing races, and other functional elements, including driving pinions or camshaft adjusting hubs, and like devices, a number of connecting methods can be provided.

Among other things, one method includes plastically expanding the tubular shaft in portions by applying a high internal pressure in order to achieve a firm fit of the components. An exposed portion of the tubular shaft can be subjected to a high internal pressure and plastically deformed by using suitable probes in individual longitudinal portions inside the components. In addition, or in the alternative, the tubular shaft, together with the components, can be placed into a die and subjected to high internal pressure along its entire length.

In addition, or in the alternative, another method is to shrink the components thermally on to the tubular shaft. Furthermore, tubular shafts can be provided with seat regions for the components, the seat regions having an increased diameter to axially slide the components with a press fit on to the tubular shaft.

The above-mentioned methods can include components whose through-hole is machined in a chip-forming way to be able to ensure suitable firm fit conditions. After the latter have been produced, it can be appreciated that the complete camshaft can be machine-finished.

In DE 34 33 595 A1, a method of producing assembled camshafts is described wherein laser welding or laser soldering is provided between the cam discs or bearing races and the hollow shaft or carrier tube. The apertures of the cam discs or bearing races correspond to the outer cross-section of the carrier tube, so that a sliding fit is achieved. To ensure mutual holding or fixing, the components are inserted into the device. This can only be achieved if internal through-welding or internal through-soldering takes place from the inside of the hollow shaft or carrier tube.

In EP 0 295 281 B1, a method of producing assembled camshafts is described wherein individual cam discs are centered in adjustable holding devices with respect to their cam bores relative to a longitudinal axis which, at the same time, forms the longitudinal axis of the holding device for the tubular member, which holding device is inserted into the cam discs. Inside the cam discs, the tubular member is then expanded in portions by internal high pressure forming in order to form press fit connections between the cam discs and the tubular member.

In EP 0 313 565 B1, a method of producing a camshaft is described wherein, round cam rings of a uniform wall thickness are formed in a die into the cam shape. At the same time, an inserted tubular shaft is formed by an internal high pressure forming process into the cam rings. The fact that the initially round cam rings have to be deformed in this way does not allow the use of materials with a high wear strength for the functional face.

In DE 101 500 093 C1, a method of producing assembled camshafts is described wherein cam rings, having a uniform wall thickness and a finish-formed functional face, are slid on to a tubular shaft. The components are subsequently inserted into a die in which the tubular shaft is shaped by internal high pressure forming into the cam rings in a force-locking and positive form-fitting way.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a method of producing assembled camshafts wherein the number of machining stages can be reduced. The objective can be achieved by a method of producing assembled camshafts from a tubular member and components which are slid onto the tubular member, and have through-holes and outer functional faces, such as cam discs and bearing races. The tubular member can be clamped in so as to be centered on a reference axis B, and the components can be slid on to the tubular member by means of their through-hole and centered via their outer contour on the reference axis B of the tubular member. In addition, a joining gap between the through-holes and the tubular member can be provided, and a material locking connection can be produced between the components and the tubular member. The material locking connection is preferably produced under adding of material and can be limited to annular regions in the joining gap at the axial ends of the components. In addition, after the production of the material locking connection which, more particularly, can include laser welding, later soldering or gluing, the largely machine-finished outer contours of the components are provided in their accurate positions relative to the reference axis of the tubular member, so that any subsequent machine-finishing, such as grinding, is not necessary to compensate for positional errors of the components relative to the reference axis, but can be provided for surface improving purposes. Preferably, care should be taken to ensure that during laser soldering or laser welding, the tempering temperature of the components in the running face and functional face is not exceeded.

In addition, or in the alternative, a second solution comprises providing a method of producing assembled camshafts from a tubular member and components slid on to the tubular member and having through-holes and outer functional faces, such as cam discs and bearing rings. The tubular member can be clamped in so as to be centered on a reference axis B, and the components can be slid on to the tubular member by means of their through-holes and centred via their outer contours on the reference axis B of the tubular member. In addition, a joining gap can be provided between the through-holes and the tubular member. Thereafter, a press fit connection can be produced between the components and the tubular member by plastically expanding the tubular member. The tubular member is preferably expanded only in longitudinal portions associated with the components, and at the same time as the press fit connection is produced. Accordingly, it is possible to produce a positive form-fitting connection, which can be provided by a particular surface roughness of the through-holes. In one embodiment, the outer contour of the components can be substantially machine-finished, independently of the shape and position of the through-holes, and can be positioned in accordance with each of their respective functions on the reference axis of the tubular member. Thus, the final position of the individual components and their functional faces relative to one another can be provided with a high degree of quality after the forming operation.

At least one method according to the invention reduces or eliminates stringent production tolerances in the through-holes and at the tubular member from the tolerance range and compensates for the joining gap which can be of a non-uniform width around the circumference. As a result, production can be less refined. In addition or in the alternative, in another embodiment components can be provided whose through-holes are machined by a non-chip-forming method, thereby eliminating a typical machining operation. In addition or in the alternative, the joining operation can include providing components with an already finish-machined outer contour. For example, cam discs and bearing races can be provided with a machine-finished running face. Accordingly, it would be unnecessary for the assembled camshaft to be clamped in again after the joining operation.

The inventive methods are particularly suitable for forged cams with punched-out through-holes, and can avoid the need for subsequent machining operations after the ejecting or punching operation. Even a broaching operation for the through-hole can be eliminated or reduced if use is made of the inventive method.

In one embodiment, a method according to the invention can be performed in the same way for cast cams and sintered cams with a formed through-hole which, again, do not require any subsequent machining operations on the through-hole after the forming process.

In another embodiment of a method according to the invention, a tubular member is used, having an outer face, which, at least in the region of the components, is produced by a non-chip forming operation. In addition, the tubular member, can be clamped via its inner face so as to be centred on its inner axis (A_(Zentren)) which inner axis (A_(Zentren)) forms the reference axis B. With this method, it is possible for the bearing regions at the tubular shaft to be ground after the camshaft has been joined together.

In another embodiment of a method according to the invention, a tubular member is used, having an outer face which, at least in the region of bearing places, has undergone a chip-forming operation. In addition or in the alternative, the outer face can be ground, and the tubular member can be clamped in via the bearing places so as to be centred on its bearing axis (A_(Lager)) and that the bearing axis (A_(Lager)) forms the reference axis B. Accordingly, further machining operations on the tubular shaft after the camshaft has been joined together can be avoided.

In a variant of at least one of the above-described embodiments, the tubular shaft can be internally clamped via the end apertures, whereas a second variant, having ground bearing places, the already ground bearing places can be clamped externally. The latter situation is advantageous for subsequently expanding the tubular member by an internal high pressure forming operation.

In order to provide a joining gap which is suitable for aligning the components on the tubular shaft in accordance with the invention, a difference of at least 0.2 mm is preferably provided between the through-hole of the cam disc and the outer diameter of the tubular member. The joining gap can then be bridged by laser soldering or laser welding with welding or soldering added material. The same process can be applied for gluing. When joining the parts by expanding the tubular member, it is preferable and may be necessary to provide a joining gap in order to permit a permanent plastic expansion of the tubular member. In one case, the joining gap can be closed due to the deformation of the tube. In the case of this selected technology, the center of the through-hole of the component may not necessarily be positioned centrally relative to the outer face of the tubular member which forms the general longitudinal axis A of the tubular member.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive method will be illustrated and explained below with reference to drawings showing the different production phases.

FIG. 1 illustrates a portion of an unmachined tubular member with a cam disc and a bearing race

a) prior to the production of the material locking connection, and

b) after the production of the material locking connection.

FIG. 2 illustrates a portion of a tubular member with finish-machined bearing places with a slid-on cam disc

a) prior to the production of the material locking connection, and

b) after the production of the material locking connection.

FIG. 3 illustrates a portion of the tubular member with finish-machined bearing places with a slid-on cam disc

a) prior to the production of the press fit connection, and

b) after the production of the press fit connection.

DETAILED DESCRIPTION

FIG. 1 a shows a portion of a tubular member 21 which comprises a welded or seamlessly drawn tube with an outer face 22 as produced and an inner face 23 as produced. The outer face can define the general longitudinal axis A of the tubular member 21. During the first production stage characterised by the number 1, the tubular member 21 can be fixed relative to a reference axis B via its inner face 23, with two points 41, 42 being provided for this purpose. The reference axis B of the clamping device for the tubular member can be defined by the central axis of the points 41, 42. The condition of the outer faces 22, 23 as produced is indicated by a corresponding simple surface symbol. The reference axis B of the clamping device for the tubular member 21 corresponds to the clamping axis A_(Zentren) and, in the case of wall thickness errors, can deviate from the general longitudinal axis A.

In a second process stage marked by the number 2, a cam disc 31 with a finish-machined running face 32 and a bearing race 35 with a finish-machined running face 36, which previously had already been slid on to the tubular member 21, can be aligned by suitable jaws 43, 44 by means of their outer contours K31, K35 on the reference axis B of the clamping device of the tubular member 21. The unmachined through-holes 33, 37 of the camshaft 31 and of the bearing race 35 typically do not play a part in the alignment process, so that it is possible for there to occur compensating and joining gaps 34, 38 which, around their circumference, comprise non-uniform widths. The machine-finished running faces 32, 36 and the through-holes 33, 35 are marked by suitable surface symbols. The through-holes 33, 35 can be machined by a non-chip-forming operation or punched out among other things.

In FIG. 1 b, any details identical to those of FIG. 1 a have been given the same reference numbers. To that extent, reference is made to the preceding description. During a third process stage which has been given the number 3, the joining gaps 34, 38, in the vicinity of the end faces 29, 30; 49, 50 of the components 41, 35, can be filled in with solder fillings 25, 26, 27, 28. When solidified, with the solder fillings preferably project only slightly beyond the end faces of the camshaft 31 and of the bearing race 35 respectively.

FIG. 2 a shows a portion of a tubular member 21 comprising a welded or drawn tube, which portion comprises an unmachined, inner face 23 as produced and an outer face 22 which can be subsequently machined by a chip-forming operation in individual bearing places 24. More particularly, the bearing places can be ground. The surface quality is marked by suitable surface symbols. The axis A_(Lager) of the bearing places 24 can, optionally, deviate from longitudinal axis A of the tubular shaft, which axis is defined by the outer face 22 as produced. In a first process stage marked by the number 1, the tubular member 21 is clamped in by suitable jaws 45, 46 in the region of the bearing places 24 and centered on the reference axis B which, corresponds to the bearing axis A_(Lager). In a second process stage, marked by the number 2, the cam disc 31 which can already have been slid-on, is centered via its outer contour K31 by jaws 43, 44 on the reference axis B of the clamping device of the tubular member 21. The unmachined through-hole 33 of the cam disc 31 may not play a part in this centring process, so that there may occur a compensating and joining gap 34 which comprises a circumferentially non-uniform width. On the cam disc 31, surface symbols indicate the finish-machined, more particularly ground running face 32 and the broken-out or punched-out through-hole 33.

In FIG. 2 b, any details identical to those shown in FIG. 2 a have been given the same reference numbers. Therefore, reference is made to the previous description. In this embodiment, too, the joining gap 34, in a third process stage marked by the number 3, at both end faces 29, 30, can be filled with annular solder fillings 25, 26. When solidified, the solder fillings preferably project only lightly beyond the end faces of the cams disc 31.

FIG. 3 a shows a portion of a tubular member 21 comprising a welded or drawn tube, which portion comprises an unmachined inner face 23 as produced and an outer face 22 which can be subsequently machined by a chip-forming operation in individual bearing places 24. More particularly, the bearing places can be ground. The surface quality is marked by suitable surface symbols. The axis A_(Lager) of the bearing places 24 can, optionally, deviate from longitudinal axis A of the tubular shaft, which axis is defined by the outer face 22 as produced. In a first process stage marked by the number 1, the tubular member 21 can be clamped in by suitable jaws 45, 46 in the region of the bearing places 24 and centered on the reference axis B which, corresponds to the bearing axis A_(Lager). In a second process stage marked by the number 2, the cam disc 31 which can already have been slid on, can be centered via its outer contour K31 by jaws 43, 44 on the reference axis B of the clamping device of the tubular member 21. The unmachined through-hole 33 of the cam disc 31 may not play a part in this centering process, so that there may occur a compensating and joining gap 34 which comprises a circumferentially non-uniform width. On the cam disc 31, surface symbols indicate the running face 32, which can be machine-finished, or ground among other things, and the through-hole 33, which can be broken-out or punched-out.

In FIG. 3 b, any details identical to those shown in FIG. 3 a have been given the same reference numbers. Therefore, reference is made to the previous description. In this embodiment, too, the joining gap 34, in a third process marked by the number 3, has permanently been reduced to zero due to the tubular member 21 in the region of the expansion region 39 inside the cam disk 31 having been plastically radially expanded. Therefore, between the expansion region 39 and the through-hole 33, a press fit connection can be provided. 

1. A method of producing assembled camshafts comprising providing a tubular member (21) and components slid on to same and each having a through-hole (33, 37) and an outer functional face (32, 36), said components selected from the group of at least one cam disc (31) and at least one bearing ring (35); wherein, the tubular member (21) is clamped in so as to be centred on a reference axis (B); wherein the components (31, 35) are slid on to the tubular member (21) by means of their through-hole (33, 37) and are centred via their outer contour (K31, K35) on the reference axis (B) of the tubular member (21); wherein a joining gap (34, 38) is provided between the through-holes (33, 37) and the tubular member (21); and a material locking connection is provided between the components (31, 35) and the tubular member (21).
 2. A method according to claim 1, further comprising adding material to provide a material locking connection between the components (31, 35) and the tubular member (21).
 3. A method according to claim 1, further comprising providing the material locking connection produced in the form of an annulus at each of the axial end faces (29, 30; 49, 50) of the components (31, 35).
 4. A method of producing assembled camshafts from a tubular member (21) and components slid on to same and having a through-hole (33, 37) and an outer functional face (32, 36) said components selected from the group of at least one cam disc (31) and at least one bearing ring (35); wherein the tubular member (21) is clamped in so as to be centred on a reference axis (B); wherein the components (31, 35) are slid on to the tubular member (21) by means of their through-hole (33, 37) and are centred via their outer contour (K31, K35) on the reference axis (B) of the tubular member (21); wherein a joining gap (34, 38) is provided between the through-holes (33, 37) and the tubular member (21); and thereafter, between the components (31, 35) and the tubular member (21), a press fit connection is provided by plastically expanding the tubular member (21).
 5. A method according to claim 4, wherein the tubular member (21) is expanded only in longitudinal portions associated with the components (31, 35).
 6. A method according to claim 4, wherein a form fitting connection is simultaneously produced between the components (31, 35) and the tubular member (21) in the region of the press fit connections.
 7. A method according to claim 1, wherein the components (31, 35) are provided so as to comprise through-holes (33, 37) produced by a non-chip forming operation.
 8. A method according to claim 1, wherein the components (31, 35) have functional faces (32, 36) which are machine-finished.
 9. A method according to claim 1, wherein the tubular member (21) has a portion of its outer face produced by a non-chip forming operation at least in the region of the components (31, 35), wherein said tubular member (21) is clamped in via its inner face (23) so as to be centred on its inner axis (A Zentren) and wherein said inner axis (A Zentren) forms the reference axis (B).
 10. A method according to claim 1, further comprising providing the tubular member (21) with an outer face receiving a chip-forming operation at least in the region of bearing places (24) on the outer face and a grounding operation; and wherein the tubular member (21) is clamped in via the bearing places (24) so as to be centred on its bearing axis (A Lager) and that the bearing axis (A Lager) forms the reference axis (B).
 11. A method according to claim 1, further comprising providing the components (31, 35) with punched-out through-holes (33, 37).
 12. A method according to claim 1, further comprising forming the components (31, 35) of materials selected from the group of sintered material and cast material with formed through-holes (33, 37).
 13. A method according to claim 1, further comprising providing a joining gap (34, 38) based on a diameter difference of at least 0.2 mm between the through-hole diameter of the components (31, 35) and the outer diameter of the tubular member (21) in the joining region.
 14. A method according to claim 1, further comprising forming a material locking connection from a connecting process selected from the group of laser soldering, laser welding and gluing.
 15. A method according to claim 14, wherein the group comprises the laser soldering and laser welding operation, and wherein the tempering temperature of the respective material is not exceeded by the connecting process in the functional faces (32, 36) of the components (31, 35).
 16. A method according to claim 4, wherein the plastically expanding step comprises hydraulic internal high pressure forming.
 17. A method according to claim 1, further comprising machine-finishing the functional faces (32, 36) of the components (31, 25) after the providing of the material locking connection.
 18. A method according to claim 17, wherein the machine-finishing is selected from the group of grinding and surface finishing. 